Meeting Abstract
148.3 Monday, Jan. 7 Sticking necks out: A novel sesamoid bone in crocidurine shrews LIN, Y.F.*; LU, T.W.; DUMONT, E.R.; LEE, L.L.; University of Massachusetts, Amherst; National Taiwan University; University of Massachusetts, Amherst; National Taiwan University yifen@bio.umass.edu
Sesamoid bones develop in tendons or other connective tissues that are subject to stress and are thought to function to diminish friction, distribute loads and alter muscle force vectors. However, the effect of sesamoid bones on performance is rarely tested experimentally. In this study, we combined anatomical, behavioral and biomechanical analysis to examine the function of a newly-found sesamoid bone in axial skeleton of shrews. This novel sesamoid bone is embedded in the nuchal ligament over the 2nd thoracic vertebra (T2) in Crocidura shantungensis, C. tanakae, C. rapax, Suncus murinus, Scutisorex somereni (subfamily Crocidurinae) but not in Episoriculus fumidus, Chodsigoa sodalis, Anourosorex yamashinai, and Blarina brevicauda (subfamily Soricinae). The T2 sesamoid bone supports the origin of splenius muscle, which attaches to the skull and controls head movement. Postural and behavioral analysis demonstrated that the necks of C. shantungensis and C. tanakae are significantly more flexible (p = 0.015), and they stick necks out more frequently (55 times/hour) during routine activities than does E. fumidus (16 times/hour). We modeled the mechanical advantage of splenius during postures used by the three species, and found that mechanical advantage was more than twice as high in Crocidura spp.. We also modeled the mechanical advantage of splenius in Crocidura with and without the sesamoid bone, and found that the presence of the sesamoid bone greatly enhances mechanical advantage (p < 0.001). To our knowledge, this is the first sesamoid bone reported from the axial skeleton and we have demonstrated its function in neck extension among crocidurine shrews.
